Inflatable slides for evacuating, in particular, commercial fixed-wing aircraft are well known. Such slides typically are stowed on-board aircraft in uninflated states and mounted on, in, or near exit doors. When the doors are opened in particular manners (as in emergency situations), the slides are designed to inflate automatically for use by passengers and crew in exiting the craft. The slides are especially useful when a passenger cabin is substantially higher than the ground or other surface on which the aircraft rests, as otherwise passengers might be required, at their peril, to jump from the cabin (or wings) of the aircraft to the resting surface.
Descent speed of persons using an evacuation slide is, at least in part, a function of the angle (α) formed between the slide and the resting surface. Shallow angles may slow descent speeds below desired minimums, resulting in unacceptably-long evacuation times. Steep angles too may be unacceptable, either increasing descent speeds above desired maximums (thus increasing possibility of injuries to persons using the slides) or causing persons to refuse to use the slides entirely.
Static measurements may be made to assist designers in determining suitable lengths of inflated slides. For example, for an aircraft at rest on the ground with its landing gear deployed, the vertical distance between the ground and an exit door may readily be measured. By selecting a particular value for angle α, the designer readily may calculate, for this static case, the minimum slide length necessary for the slide to contact the ground.
Unfortunately, however, need to use an aircraft evacuation slide may arise in situations other than as described above. Failure of landing gear either to deploy or to support an aircraft could, for example, change the attitude of the aircraft such that one or more exit doors are higher (or lower) than in the static case. Similarly, if the resting surface of the aircraft is not uniformly horizontal, vertical heights of exit doors above the resting surface may differ from their norms. Yet additionally rupture and, for example, roll of the fuselage could increase beyond normal the height of some doors above even a level resting surface. As a consequence, a slide whose length has been selected based on static conditions may be of inadequate length when deployed for actual use.
U.S. Pat. No. 6,814,183 to Horvath, et al. seeks to resolve this issue by providing an extendable evacuation slide “deployable in either a foreshortened or lengthened configuration.” See Horvath, Abstract, 11. 2-3. Deployment configuration is determined automatically, so that it “does not rely on manual actuation or physical measurement of the distance to the ground.” See id., col. 2, 11. 28-29. Instead, an “electronic sensor such as an inclinometer” informs a control circuit as to “whether the aircraft is in a horizontal attitude, a nose down attitude or some other attitude.” See id., 11. 48-49; col. 5, 11. 6-8. Should the control circuit indicate the slide should be extended, a pyrotechnic cable cutter may be used to release the extendable portion of the slide. See id., Abstract, 11. 7-10.
Deployment state of the system of the Horvath patent is determined upon initial deployment. Stated differently, only one deployment decision is made based on information from the inclinometer: Either only the main section of the slide is inflated or both the main and extendable portions are inflated together. Consequently, if the signal from the inclinometer is erroneous (either electrically or practically), the extendable portion may inflate undesirably with no opportunity for correction.
For example, some evacuations follow collapse of the main (rearward) landing gear of aircraft, which event may lead to a phenomenon known as “tail tipping.” Such a tail tip subsequent to the inclinometer sensing aircraft attitude could adversely impact operation of the automatic system of the Horvath patent toward the rear of the aircraft. If the control circuit determines that both the main and extendable portions of the slide at a rear door should be inflated, they will do so together. However, any subsequent tipping of the aircraft tail could render the slide length too long for satisfactory use by passengers—i.e. the increased length would make angle α less than desired—with no way to prevent inflation of the extendable portion or automatically deflate it. By contrast, if only the main portions of slides at the forward doors are inflated based on the inclinometer readings, the subsequent tail tip may render them too short for use (i.e. angle α would be greater than desired) with no opportunity for extension.
Because the main and extendable portions of the slide of the Horvath patent are configured to be inflated together when signaled, no bulkhead or other mechanical fluid-interruption device is incorporated into the tubes of the slide. Instead, the extendable portion of the slide is laced into a pouch positioned at an end of the main portion, with the pyrotechnic cable cutter severing the lacings if extension is signaled to occur. As the lacings are external to the slide, however, they conceivably could be severed unintentionally (and undesirably) by sharp debris or heat. Need thus exists for extendable evacuation slides in which inflation of extendable portions occurs separately from inflation of the main portions and which are configured both to limit possibility of simultaneous inflation of the portions and to reduce possibility of the slides extending when not desired.